When the flammable refrigerant leaks indoors, there is a fear in that an indoor refrigerant concentration increases to cause formation of a flammable concentration region.
In Patent Literature 1, there is described an air conditioning apparatus including an outdoor unit, a heat medium relay unit, and an indoor unit. In the air conditioning apparatus, the heat medium relay unit is installed in a space such as a space above a ceiling, which is inside a building but different from an indoor space. A relay unit fan for ventilation inside a casing is provided in the heat medium relay unit. Further, an opening port is formed in the casing of the heat medium relay unit at a position from which air from the relay unit fan escapes. The relay unit fan is driven, for example, all the time (including a period of time of stopping an operation of the air conditioning apparatus) with the airflow rate equal to or higher than the ventilation air flow rate to suppress the refrigerant concentration inside the casing of the heat medium relay unit to be lower than a lower limit flammable concentration.